How to create reusable Python component
You could save the file into the site-packages directory, which is found by going to your Blender folder and then 2.70 > python > lib > python3.3 > site-packages.

Say your file is called "Foo.py" and has in it a function

def X(p,q):
    return p + q


then, after saving it into site-packages, in the Blender text editor or console, you could use:

from Foo import X